Integrated circuits are manufactured from semiconductor wafers that are conventionally round in shape and made of highly brittle silicon. Such wafers are subjected to a variety of processing steps in transforming the semiconductor wafer into integrated circuit components. The various processing steps must be performed under ultra-clean conditions to minimize the potential of contamination of the wafers as they are being processed. Each wafer may be subjected to dozens if not hundreds of steps in its processing cycle. The potential for contamination and destruction of a wafer or reduction in yield is ever present throughout the various processing and packaging steps. Particularly during the steps that take place at fabrication facilities any minute particulates can destroy the integrated circuit on which it falls. Once the processing steps of the wafers are completed they are generally shipped while still in wafer form to a facility that will dice and capsulate in integrated circuit packaging each individual circuit on the wafer.
The stringent particulate control that takes place during the processing steps is generally not necessary in shipping the completed wafers to the facility that dices and packages the individual circuits.
Traditionally, during the processing and storage and shipping of semiconductor wafers the wafers are supported and constrained at their edges to prevent any contact and possible damage and contamination to the faces of the wafers having the circuits thereon.
Even as semiconductor wafers are getting larger in scale, now up to 300 millimeters in diameter, the density of components is getting significantly greater. Moreover, disks are also are getting thinner providing much thinner completed integrated circuit packages. This has been driven, at least in part, by the cellular phone industry that has sought thinner cell phones.
Accompanying the trend towards larger, more dense and thinner wafers, the wafers are becoming more valuable, more brittle, more easily damaged during shipment. Although it is possible, desirable, and common to ship thicker wafers in enclosed containers that would support the wafers exclusively by their edges, using such devices to ship the thinner wafers has proven problematic due to breakage and damage of the wafers. Foam material, such as urethane, is used to cushion the top and bottom of the stack.
Thus for the thinner more fragile wafers, enclosures are utilized which have the wafers axially stacked on top of one another and separated by layers of paper-like flexible sheet material. Thus the support of each wafer is by adjacent wafers and the entire stack of wafers.
Referring to FIG. 1, prior art wafer carrier as illustrated in U.S. Pat. No. 5,553,711 to Lin discloses a container that has a base, upright sidewalls defining a circular pocket, wafer dividers and a cover that comes down and threadingly attaches to the base.
FIG. 2 discloses a conventional wafer carrier in which the enclosure is defined by a cookie tin like plastic container having a bottom 40, a top lid 42 and utilizing a circular urethane foam bottom cushion 44, and sheet material 49 interspersed between wafer 50.
Referring to FIGS. 2 and 3, another wafer shipper is disclosed for shipping the stacked wafers with dividers therebetween. This wafer shipper has a base 52 and a top cover 54. The base and top cover are injection molded and have circular shaped and axially extending structural members 56, 58 in the base component. Similarly, the top cover has axially extending circular structural members 59 and 60 and radially extending ribs 66, 69 that also project axially.
These stacking wafer shippers may be both manually handled as well as robotically handled. Thus, means for opening and closing such containers must be both manually and robotically operable and for manual purposes should be intuitive as well as simple, reliable, and quick. Various means are known for latching such wafer shippers. These include threads such as shown in prior art FIG. 1, a snap-on seal as shown in prior art FIG. 2, a minimal rotation thread, and axially projecting spring latches.
The wafer shippers that use the threaded engagements are awkward and subject to misalignment and improper attachment. These wafer shippers visually appear symmetrical in at least two planes and therefore there are typically four different options in assembling a top cover to a bottom cover. However, conventional prior art shippers generally require that the top cover be assembled in a specific orientation for proper latching.
U.S. Pat. No. 6,193,068 to Lewis, et al. discloses axially extending spring latches and utilizes a double wall to define the pocket for the stack of wafer carriers. Said double wall thickness is defined by two spaced thin wall sections which are not attached to one another extending from the base. This configuration appears to allow the individual unsupported thin walls supported only at the base to take on and retain deformation. The concentric arrangement of the thin walls makes any such deformation visibility apparent. The double sidewall in this prior art embodiment may help to isolate direct impact on the top cover from direct communication from top cover structure to the wall defining the wafer pocket.
In the embodiment shown in FIGS. 7, 8, 9, and 10, any separation stress will occur as illustrated by G in FIG. 11. Such loading of the wafer shipper also can cause the deformation of the otherwise planar corners of the base to be stressed out of position causing wobbling when placed on a planar surface and error in seating when placed on a machine interface. Such deformation can be caused in part by an overloading condition and also in part by the structural configuration of the wafer shipper.
It would be desirable to provide sufficient structure in the base of such wafer shipper to prevent such distortion and bowing. Moreover, it would be highly desirable to provide a wafer carrier that has indicating means therein to prevent such an overloaded condition.
Referring to FIGS. 12, 13, 14, and 15 a further prior art wafer shipper is shown. This wafer shipper has stunted threads 82, 84 that allow the wafer carrier to be rotated less than 30xc2x0 to accomplish the latching. This wafer carrier has the difficultly of requiring relatively precise angular positioning for initial placement of the top cover on the base before said rotation.
This embodiment utilizes axially projecting double thin wall similar to the prior art embodiment of FIGS. 8, 9 and 10, although the double sidewalls are connected at the ends of each segment. Thus, four separate wall portions are defined all of which are distinct from one another and integral with the base. Due to the connecting portions 94 which connect each of the pairs of thin sidewall segments, a direct impact blow on the top cover will transmit the force of such blow directly from the top cover through said connecting portions 94 to the wafers. This top cover also has features configured as nubs, which may engage a floppy disk. See FIG. 16 that is a cross-sectional of the wall at one of said nubs.
Generally all embodiments of the wafer carriers herein will be injection molded of thermoplastic material such as polypropylene. Such material requires structure such as ribs and channels for rigidity.
In that these shippers do not have the severe particulate control issues that are necessary for carriers in the fab processing environment, it is not necessary to have hermetic sealing. In fact, such hermetic sealing is inimical to robotic handling and easy manual handling, specifically the opening and closing of the shippers. Still it is important to have the interface between the top cover and the base to provide as good of sealing characteristics as possible. Moreover, it is important to eliminate or reduce any bowing that occurs along one of the sidewalls intermediate the corners of the top cover or the base.
These types of containers may be utilized once and thrown away or may be recycled and utilized multiple times. Although the product shipped in such containers can be of immense value, it is still important to reduce the manufacturing cost of the shippers to as great as extent as possible, consistent with the other necessary characteristics.
A most important characteristic of such wafer shippers for stackable wafers is that the shippers provide protection from damage due to shock during the transportation. This shock may consist of direct impact with the shipper""s top cover or base or consist of jarring of the entire shipper package. In either case it is important to provide protection from damage to the wafers packed therein.
Moreover, it is important that such wafer shippers provide latching means of high integrity that do not inadvertently open during shipment or handling, for example when a shipper is inadvertently dropped.
Such shippers are typically drop tested to determine the overall integrity of the shipper. Upon such dropping, unlatching, breakage of the shipper or damage to the wafers constitutes a failure. The impact during dropping, including drop testing, creates shear, compressive and torsional forces on the shipper components. The shipper, including the latches must withstand combinations of these forces when loaded.
These wafer carriers rely heavily upon the separation of materials between wafers, which may be polyethylene sheet material with carbon providing a static dissipative characteristic, polyurethane foam, or other suitable flexible thin sheet material. Typically the packing material placed on the bottom and top of the stack will be the polyurethane foam that is compressible. The compressibility of the foam facilitates packing a variable number of wafers in a particular shipper which can leave some undesirable discretion to the packer as to how many wafers and/or how much padding material is appropriate for a particular shipper. Moreover, inserting excessive or even a full load of wafers and foam padding can, in prior art wafer shippers, particularly those with latches on the diagonal corners, cause distortion and/or bowing of the top cover and/or base. This bowing may actually cause a gap between the top cover and base. Such a gap is visually undesirable, may provide a pathway to contamination of the contents, and may further affect the integrity of the container during impact or shock, causing breakage or unlatching. If the shipper is underpacked with foam or other packing material, breakage may occur at limits under normal impact limits. Known prior art wafer carriers have provided no ready assistance in identifying an appropriate range of foam and wafer stacked thickness which is optimal for providing security to the wafers. Similarly the stacked wafer shippers with the latches on the diagonally opposite corners have provided no means to minimize the visibility of the gap at the sides of the shipper when the shipper is fully loaded or slightly overloaded. Moreover, these prior art shippers have inadequately provided structural means to the base and top cover to provide rigidity and minimize said bowing and gaps at the interface.
A wafer shipper for stacked wafers provides significantly improved resistance to shock and impact as well as flexibility and tolerance in wafer capacities and guidance in optimal amount of packing material. These characteristics are provided by unique structural configurations that provide rigidity and desirable distribution of impact forces. The shipper has a base and a top cover both of which have a nominal wall that primarily forms all of the features of the respective components. The base has four sides, four corners, and arcuate wall segments defining a wafer stack pocket. The sides are formed of a downwardly extending nominal wall portion and an upwardly extending lip. Both adjoin a nominal base wall which includes a planar bearing surface that extends around the base, outside the arcuate wall segments, and forms a seat for the top cover. The planar bearing surface adjoins the arcuate wall segments and also adjoins the upright stop portions which are part of four shoulders positioned at the corners of the base. Each of said shoulders extends to the side wall. Channels formed from the nominal base wall extend downwardly from the floor of the wafer stack pocket. The channels extend primarily radially or chordially.
The top cover has a continuous nominal side wall extending around the four sides. The sides adjoin the top cover top wall which includes recessed nominal wall structure providing rigidity to the top cover, as well as the stack top engagement surfaces. Four ears extend outwardly at the corners and include oversided latch slots recessed structure and latch retention means. An upper lip at the top cover perimeter extends upwardly and is sized slightly less than the downwardly extending wall of the base so that several shippers may be stacked.
A feature and advantage of particular embodiments of the invention is the unique form fit whereby impact forces that are received on the corners and/or sides of the top cover are transferred to the base through the top cover to upright portions on the opposite side of the base from where the impact occurs. There is not a direct horizontal shock conduit from the corners or sides of the top cover to the adjacent portions on the base. This provides a significant improvement in the robustness of the container as well as significant improvement in the protection provided to the wafers, as well as much better resistance to unlatching upon such impact.
A further feature and advantage of particular embodiments of the invention, an additional concentric set of arcuate wall segments of a lesser diameter are provided. These may cooperated with the first set of arcuate wall segments to provide a double wall for additional strength for resisting fracturing or damage to the wafers during occurrences such as dropping. Moreover, said second wall can be utilized to make a mold for molding a wafer carrier for a first size of wafers convertible into a mold for molding wafer carriers for a second sized of wafers, said second size smaller than the first. The convertible feature can be added by forming the appropriate concentric slots in the mold for the wafer carrier for the first size. Said appropriate concentric slots, are sized for the second size wafers. Suitably sized blanks may be inserted in said slots when the mold is to be used for the first size wafer carrier and the blanks may be removed when the mold is utilized for the second size. More broadly stated a mold for a wafer carrier can utilize separate inserts for converting from a first size pocket to a second size pocket.
A feature and advantage of the invention is that a single mold can be utilized for different carriers for carrying different size wafers. Moreover such a mold will provide a single footprint. Such a single footprint will facilitate automated handling with less changeover of equipment when wafer sizes are changed. Such a single footprint will allow stacking of carriers for different size wafers in a single stack. Moreover, shipping such single footprint carriers will be easier and less expensive in that packaging and cushioning material, which is often specifically sized for a particular carrier, is more universal.
A feature and advantage of particular embodiments of the invention is that it is easier to mold than other prior art wafer carriers that have structural rigidity members. Conventional ribs cause shrinking problems.
A further feature and advantage of particular embodiments of the invention is that the nominal wall rigidity members also are utilized to create a pocket for memory disks, either 3xc2xd floppy disks or CD""s.
A further feature and advantage of particular embodiments of the invention is that radial channels formed from the nominal wall provide significantly better resistance to twisting of the components and particularly the base.
A further feature and advantage of particular embodiments of the invention is that a labyrinth seal is provided along the sides of the assembled shipper at the interface between the top cover and the base.
A feature and advantage of particular embodiments of the invention is that the latching arm extending from the base has a horizontal component to provide greater elongation capabilities of said arm. Such provides a latching force that remains consistent under a wider range of loads than conventional latching arms that extend directly and only vertically from the base. That is, the spring constant is effective over a greater distance that conventional latch arms.
A feature and advantage of particular embodiments of the invention is that the nominal wall is utilized for providing structural rigidity rather than ribs. The nominal wall is configured into straight channels rather than circular channels concentric with the wafer pocket that are known in the art. The straight channels are oriented radially or chordially on the base and top cover. Where there are multiple fastening locations connecting the base to the top cover, for example four or more, that are circumferentially spaced around the wafer pocket, the concentric circular channels are appropriate. However, where there are two fastening locations positioned diagonally across from each other at the corners of the base and top cover, the structural rigidity and resistant to twisting of the base appear to be significantly improved when the radially and/or chordially extending channels are utilized.
A further feature and advantage of particular embodiments of the invention is that sidewall extending from the top cover has a single nominal wall with a shape, from the plan view, having four straight sidewalls and abbreviated corners that have inwardly extending channels. Such a configuration provides a significantly greater rigidity than conventional simple shapes, cylindrical or square, and utilizes substantially less material that double reinforced walls known in the art.
A further feature and advantage of particular embodiments of the invention is that same is easier to mold consistently and utilizes significantly less material than prior art stacked wafer shippers.